1. Field of the Invention
This invention relates to a flat transducer which employs a thin plate of a piezoelectric substance. It is useful for audio microphones or loudspeakers, etc.
2. Description of the Prior Art
Recently, technologies for miniaturizing radios, tape recorders etc. and operating them with the battery drive for long periods of time have progressed, and the thin pocketable type has come into fashion. This tendency owes much to the advance of the circuit integration technology especially having supported the spread of pocketable type electronic desk calculators. The electronic desk calculators have also been equipped with small-sized sound producers developed for the alarms of wrist watches, and the input/output operations of calculations have utilized, not only display to the eyes, but also audio signals to the ears.
Now, a battery-driven electronic micro-device such as watch, calculator, radio and tape recorder trends to be provided with both a display and a sound producer and/or microphone. In this case, the display has been rendered small in size, flat in structure and low in power dissipation owing to the advent of liquid crystal. Regarding the sound producer, however, any product does not fully satisfy the requisites of a small size, a thin structure and a low power dissipation. Therefore, the need for a flat speaker has risen abruptly, and the development thereof has become the technological subject of the times.
As stated before, the sound producer required for the electronic micro-device must be small in size, flat in structure and low in power dissipation. Although a piezoelectric buzzer is excellent in points of the small size, the flat structure and the low power dissipation, it is a resonator for a signal of fixed frequency. It cannot cover a desired acoustic band as the speaker for audio signals of wide frequency band, and is very difficult to produce clear voices.
An example of the piezoelectric buzzer for watches is known from Japanese Patent Application Laid-open Specification No. 55171/1978.